<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script type="text/javascript">

    </script>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <script type="text/javascript">
        var bt=document.querySelectorAll("button");
        for(let i=0;i<bt.length;i++){
            bt[i].onclick=function(){
                console.log(i);
            }
        }
    </script>
</body>
</html>